With the advancement of contemporary technology, a variety of production techniques have been improved. Method of mass production has been developed to become fully automatic production process from the labor-intensive operation to pursue the improvement of production efficiency and reduction of manufacturing costs.
During a present production process of the display module, a width of a gap between parts of the display module needs to be measured, e.g., a gap between a central display area of the display module and a frame located at an edge of the display module. In general, a user can use a digital optical microscope with his/her eyes to measure and determine the width of the gap. However, this kind of measurement takes too much time and is not accurate enough to meet with a quality check.